Carbon dioxide (CO2) separation and capture is a global topic that is closely related to energy and the environment. For example: CO2 capture from power plant flue gases would dramatically reduce greenhouse gases and the resulting deleterious effects; CO2 extraction from low-grade natural gas is needed as an energy efficient technique to improve purity of the natural gas to pipeline standards; and captured CO2 may be used for enhanced oil recovery (EOR) processes. CO2 separation from gases and fluids also has many applications in the areas of medical science, chemical engineering, the petroleum industry and even food industries.
Most commercial CO2 separation plants use a process referred to as “pressure swing adsorption” (PSA), which is based on chemical absorption with a monoethanolamine (MEA) solvent. PSA processes require large capital equipment investment and consume high amounts of energy needed for regeneration.
Membrane separation is a compact, energy-efficient, and inexpensive alternative to PSA. Some CO2 membranes have been developed, which include porous CO2 membranes based on physical separations such as Knudsen diffusion or molecular sieving, as well as dense CO2 membranes (e.g. polymer membranes) based on chemical separation such as solubility and diffusion in the solid state. Porous membranes based on physical separations suffer from relatively poor selectivities. Additionally, physical separation depends strongly on the composition of other gases within the CO2 mixture. Deficiencies of dense CO2 membranes include a very low CO2 flux across the membrane because of the small CO2 solubility in the membrane and slow diffusion of CO2 across the membrane. In general, most current CO2 membrane technologies are not sufficiently efficient for practical applications.
An improved membrane for the effective separation of CO2 from a gas or liquid, and its method of formation and use, would be desirable.